To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the next generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, EUV lithography of wavelength 13.5 nm, and double patterning version of the ArF lithography, on which active research efforts have been made.
Chemically amplified resist compositions comprising an acid generator capable of generating an acid upon exposure to light or EB include chemically amplified positive resist compositions wherein deprotection reaction takes place under the action of acid and chemically amplified negative resist compositions wherein crosslinking reaction takes place under the action of acid. Quenchers are often added to these resist compositions for the purpose of suppressing the diffusion of the acid to unexposed areas to improve the contrast. The addition of quenchers is fully effective to this purpose. A number of amine quenchers were proposed as disclosed in Patent Documents 1 to 3.
As the pattern feature size is reduced, approaching to the diffraction limit of light, light contrast lowers. In the case of positive resist film, a lowering of light contrast leads to reductions of resolution and focus margin of hole and trench patterns.
For mitigating the influence of reduced resolution of resist pattern due to a lowering of light contrast, an attempt is made to enhance the dissolution contrast of resist film. Another attempt is also made to control acid diffusion which causes image blurs to resist patterns.
There is known a chemically amplified resist material utilizing an acid amplifying mechanism that a compound is decomposed with an acid to generate another acid. In general, the concentration of acid creeps up linearly with an increase of exposure dose. In the case of the acid amplifying mechanism, the concentration of acid jumps up non-linearly as the exposure dose increases. The acid amplifying system is beneficial for further enhancing the advantages of chemically amplified resist film including high contrast and high sensitivity, but worsens the drawbacks of chemically amplified resist film that environmental resistance is degraded by amine contamination and maximum resolution is reduced by an increase of acid diffusion distance. The acid amplifying system is very difficult to control when implemented in practice.
Another approach for enhanced contrast is by reducing the concentration of amine with an increasing exposure dose. This may be achieved by applying a compound which loses the quencher function upon light exposure.
With respect to the acid labile group used in (meth)acrylate polymers for the ArF lithography, deprotection reaction takes place when a photoacid generator capable of generating a sulfonic acid having fluorine substituted at α-position (referred to “α-fluorinated sulfonic acid”) is used, but not when an acid generator capable of generating a sulfonic acid not having fluorine substituted at α-position (referred to “α-non-fluorinated sulfonic acid”) or carboxylic acid is used. If a sulfonium or iodonium salt capable of generating an α-fluorinated sulfonic acid is combined with a sulfonium or iodonium salt capable of generating an α-non-fluorinated sulfonic acid, the sulfonium or iodonium salt capable of generating an α-non-fluorinated sulfonic acid undergoes ion exchange with the α-fluorinated sulfonic acid. Through the ion exchange, the α-fluorinated sulfonic acid thus generated by light exposure is converted back to the sulfonium or iodonium salt while the sulfonium or iodonium salt of an α-non-fluorinated sulfonic acid or carboxylic acid functions as a quencher.
Further, the sulfonium or iodonium salt capable of generating an α-non-fluorinated sulfonic acid also functions as a photodegradable quencher since it loses the quencher function by photodegradation. Non-Patent Document 3 points out that the addition of a photodegradable quencher expands the margin of a trench pattern although the structural formula is not illustrated. However, it has only a little influence on performance improvement. There is a desire to have a quencher for further improving contrast.
Patent Document 4 discloses a quencher of onium salt type which reduces its basicity through a mechanism that it generates an amino-containing carboxylic acid upon light exposure, which in turn forms a lactam in the presence of acid. Due to the mechanism that basicity is reduced under the action of acid, acid diffusion is controlled by high basicity in the unexposed region where the amount of acid generated is minimal, whereas acid diffusion is promoted due to reduced basicity of the quencher in the overexposed region where the amount of acid generated is large. This expands the difference in acid amount between the exposed and unexposed regions, from which an improvement in contrast is expected. However, this method has the drawback of increased acid diffusion.
Biguanide and phosphazene compounds are known as superstrong base compounds. Since they have a higher basicity than diazabicycloundecene (DBU), their use as a catalyst for curing reaction of epoxy compounds is under study. For example, Patent Documents 5 and 6 disclose base generators capable of generating guanidine, biguanide, phosphazene, and 2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]-undecane compounds upon light exposure. In general, the amount of acid generated by a photoacid generator increases as the exposure dose is increased. In a system where a photoacid generator and a photobase generator coexist with the amounts and generation efficiencies of PAG and PBG being equal, the amount of generated acid does not increase even when the exposure dose is increased. If the amount and generation efficiency of PAG are great, the amount of acid increases as the exposure dose is increased, but that increase is yet insufficient and so the contrast of resist is low.
Attention is now paid to the negative tone pattern forming process via organic solvent development. In an attempt to form a hole pattern by light exposure, a hole pattern having the minimum pitch can be formed by a combination of a bright-pattern mask with a negative tone resist. There is the problem that the pattern as developed varies in size due to a lapse of time, known as post exposure bake to development delay (PEBDD) or post PEB delay (PPD). The reason is that during storage of the resist film at room temperature after PEB, the acid gradually diffuses into the unexposed region where deprotection reaction takes place. One solution to the PPD problem is to use a protective group having a high level of activation energy and to effect PEB at high temperature. Since PPD is a reaction at room temperature, the influence of PPD is mitigated as the temperature gap between PEB and PPD is greater. Use of an acid generator capable of generating an acid having a bulky anion is also effective for mitigating the influence of PPD. While a proton serving as acid pairs with an anion, the hopping of proton is reduced as the size of anion becomes larger.
Another component that is expected effective for mitigating the influence of PPD is a quencher. Conventional quenchers were developed for the purpose of suppressing acid diffusion during PEB at high temperature for thereby enhancing the contrast of deprotection reaction. For mitigating the influence of PPD, it is desired from a different viewpoint to develop a quencher capable of suppressing acid diffusion at room temperature.